In order to detect any changes of enzymatic activities which could indicate a regulatory mechanism for cell metabolism, several enzymes have been assayed under growth and starvation conditions. In the first part of this work, proline oxidase, aspartate kinase and isocitrate lyase activities were measured in Saccharomyces cerevisiae grown on minimal medium and acetate but no significant changes in their specific activities could be found during stationary phase or during nitrogen or carbon or vitamin starvation. At present, the specific activities of glucose-6-phosphate dehydrogenase, pyruvate kinase, glutamate-oxalacetate transminase, glutamate dehydrogenase TPNH-dependent and glutamate dehydrogenase DPNH-dependent are being measured on yeasts grown on minimal medium and glucose. These enzymes have been first studied during logarithmic nd stationary phases of growth and are being measured now under starvation conditions.